This invention relates to an hydraulic control system for the operation of linear double-acting hydraulic motors having a cylinder bore with a blind end and a rod end, and more particularly to a closed circuit hydraulic control system for operating such motors which requires no reservoir or separate accumulator and no valve for reversing the flow of fluid in the cylinder.
It is well known that hydraulic control systems incorporating "double-ram" hydraulic motors, that is hydraulic motors having a cylinder bore with two rod ends, could be operated in a closed circuit with no reservoir or separate accumulator. Indeed, since the piston rod of such motors extends on both sides of the piston and through the cylinder ends, the volume of hydraulic fluid displaced by the piston when it moves towards one end of the cylinder is totally absorbed by the vacuum created at the opposite end of the cylinder, assuming that the volume taken by the piston rod is the same at both ends of the cylinder. It is also well known that pairs of hydraulic motors having a cylinder bore with a blind end and a rod end, that is a piston rod extending on one side only of the piston, could be operated in a closed circuit with no reservoir or separate accumulator, provided that each pair of hydraulic motors is connected to a circulating pump in such a manner that the blind end of one cylinder is connected in parallel with the rod end of the other cylinder so that the total volume of liquid displaced by both pistons may be absorbed by the vacuum created behind the pistons. However, hydraulic systems using a single hydraulic cylinder having a cylinder bore with a blind end and a rod end or plural hydraulic cylinders having a blind end and a rod end with their blind ends and their rod ends connected in parallel to a circulating pump, have always required a reservoir or separate accumulator for storing the volume of fluid taken by the piston rod when the piston moves towards the blind end of the cylinder bore.